Final answer:
In H₂, the 1s atomic orbitals of two hydrogen atoms overlap end-to-end to form a σ (sigma) bond, resulting in increased electron density between the nuclei and a more stable molecular orbital compared to the separate atoms.
Step-by-step explanation:
The type of overlap present in H₂ is the end-to-end overlap of two singly occupied hydrogen 1s atomic orbitals, which results in the formation of a σ (sigma) bond.
When two hydrogen atoms approach each other, their 1s atomic orbitals, each containing one electron, begin to overlap. The orange electron density in diagrams representing H₂ molecules illustrates an increased electron density in the region between the two positively charged nuclei. This accumulation of electron density creates an electron-pair bond, tying the two atoms together and giving rise to a molecular orbital that is lower in energy compared to the separate atomic orbitals of hydrogen, thus making the H₂ molecule more stable. The concept of molecular orbitals, such as the bonding σ0₁s orbital shown in molecular orbital energy diagrams, supports this explanation.
It is important to note that in the molecular orbital diagram for H₂, the two available electrons from the hydrogen atoms fill the bonding σ0₁s molecular orbital. Since the σ bond is symmetrical around the bond axis, it results in a strong and stable bond between the hydrogen atoms in the H₂ molecule.